Forecast the next few months from historical data in Excel
Builds a simple, explainable forecast from your past numbers, with trend and seasonality, a range, and the Excel steps to reproduce it.
The prompt
Help me forecast the next few periods from my historical data, using a method I can build and explain in Excel.
What I'm forecasting: [e.g. "monthly revenue", "weekly ticket volume", "units sold by product"]
History: [PASTE date and value columns - ideally 24+ months for monthly data]
Forecast horizon: [e.g. "next 6 months"]
Known events: [one-offs in the past (promotions, outages, COVID, lost client) and planned changes ahead (price rise, new product)]
What the forecast is used for: [e.g. "staffing plan", "budget", "inventory order"]
Steps:
1. Inspect the history: trend, seasonality, unusual spikes or dips, missing periods, and structural breaks. Say which past points should be adjusted or excluded, and why.
2. Choose the simplest method that fits, and say why: average of recent periods, linear trend (FORECAST.LINEAR / TREND), seasonal method (FORECAST.ETS or Forecast Sheet), or seasonal indexes applied to a trend.
3. Back-test: forecast the last 3-6 known periods as if they were unknown and report the error (MAPE or average % miss).
4. Produce a range, not just one number: low / expected / high, with the confidence interval if using FORECAST.ETS.
5. Layer in known future events separately, so the baseline and adjustments are visible.
Return:
- Observations about the history.
- The forecast table: Period | Baseline | Adjustments | Forecast | Low | High.
- Back-test accuracy.
- The exact Excel formulas or Forecast Sheet settings to reproduce it.
- Assumptions and the main risks to the forecast.
Use only my data. If the history is too short or noisy for a reliable forecast, say so plainly and suggest what to use instead.
Highlighted [brackets] are blanks to replace with your own details.
Fill in the blanks and use this promptMore Data & Analysis prompts
What to fill in
- e.g. "next 6 months"
- e.g. "staffing plan", "budget", "inventory order"
How this prompt is built
This prompt follows the Few-Shot structure (Few-shot prompting). A few-shot prompt includes one or more worked examples of the input and the output you want, so the model can copy the pattern instead of guessing it.
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